A conventional developing device includes a casing, a developing roller carrying developing agent thereon, a thickness regulating blade slidingly contacting the developing roller and regulating a thickness of the developing agent carried on the developing roller, and a plurality of seal members preventing the developing agent from leaking from a gap between the thickness regulating blade and the developing roller. The thickness regulating blade is provided with a press member in sliding contact with the developing roller.
The seal member includes an upper side seal located between the thickness regulating blade and the casing, and a blade side seal located at each width end of the press member. The upper side seal is configured to prevent a developing agent from leaking from a base portion of the thickness regulating blade. The blade side seal is configured to prevent the developing agent from leaking from a gap among the thickness regulating blade, the casing, and the developing roller.